In the field of plant cultivation, plants are cultivated by preparing seedling plugs, and then using the seedling plugs to grow the plants.
Seedling plugs are prepared by planting rows of adjacent seeds in a plant-growing medium in a first growth area, and providing water and light until a plant which has grown from one of the seeds sprouts above the surface of the plant-growing medium. In order to conserve space, the seeds in the initial growth area are planted quite close to one another, so that if the seeds were permitted to continue growing past the initial sprouting stage within the initial growth area, their root structures would interfere with one another and their leaves would block light from reaching the leaves of adjacent plants.
Once the seeds have sprouted, seedling plugs are created by cutting a cylinder of plant-growing medium surrounding the root structure of each young plant. These seedling plugs are then moved to a second growth area and placed in discrete containers containing loose particulate plant-growing medium, or discrete blocks of rigid plant-growing medium such as rockwool, to allow the plants to grow to sufficient maturity for sale. Once the seedling plugs have been removed from the first growth area, a new set of seeds is planted therein, so that this new set of seeds can sprout while the plants from the previous set of seeds mature, so that plants at various levels of maturity are growing simultaneously. Optionally, the seedlings may be grown to an intermediate level of maturity in the second growth area and then transferred to a third growth area where the containers are spaced further from one another and allowed to further mature. Automated mechanical handling of the discrete containers, and of the discrete blocks of rigid plant-growing medium such as rockwool, is quite common.